Although still hopeful that a compromise can be reached, Italian authorities are sharply irritated by the recent U.S. decision to extend the embargo on equipment for the Soviet Siberian gas pipeline to European companies operating with American licenses.

The U.S.-Italian relationship had been passing through a particularly happy phase ever since Italy agreed in late 1979 to accept the deployment of 112 cruise missiles here, and Italian criticism of Washington's policies is generally muted.

This week, however, Premier Giovanni Spadolini expressed "very sharp and growing concern" over recent U.S. decisions, including the embargo, which would scuttle a multimillion-dollar Italian contract to supply the Soviet Union with sophisticated machinery for the pipeline.

In a speech to the Council of European Ministers in Brussels Monday, Spadolini reacted sharply to the new measures, saying they had been "received by the Italian government with concern and anxiety." Foreign policy sources say he was dismayed by what appeared to be retrenchment on earlier understandings.

Spadolini urged "loyal application by the Americans of the agreements reached in Versailles" at the recent economic summit. These agreements also considered trade policy, particularly with regard to steel, and monetary cooperation between the United States and Western Europe. Progress was "not sufficient" in that field, he said.

The embargo on sales of U.S.-licensed goods would jeopardize a longstanding contract between the Soviets and Nuovo Pignone, a Florence-based firm owned by ENI, the state petroleum conglomerate. The Italians are to supply the Soviets with 19 pumping stations built with turbines built or licensed by General Electric.

About half of the equipment has already been produced, and the total value of the contract is estimated at about $500 million.

The embargo is expected to delay construction of the pipeline and thus deny Italy the option of ratifying a gas contract that would provide this energy-starved country with 6.8 billion cubic meters of natural gas each year.

Because of Socialist and Social Democratic opposition within Italy's five-party governing coalition, the government has avoided making a final decision on the Soviet gas offer. But it is still a live option. Furthermore, the Italians have been eager to keep the Soviet deal alive to exert pressure on Algeria--with which they are engaged in a gas-price dispute.

Foreign Ministry sources say the situation was eased somewhat by recent U.S. hints that the embargo could be lifted if Western governments tightened provision of credit to the Soviets. But, they say, resentment over an apparent lack of U.S. concern for European interests continues to rankle.